<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="utf-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>$^H - Perldoc Browser</title>
    <link rel="search" href="https://perldoc.perl.org/opensearch.xml" type="application/opensearchdescription+xml" title="Perldoc Browser">
    <link rel="canonical" href="https://perldoc.perl.org/variables/$%5EH">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css" integrity="sha384-JcKb8q3iqJ61gNV9KGb8thSsNjpSL0n8PARn9HuZOnIxN0hoP+VmmDGMN5t9UJ0Z" crossorigin="anonymous">
    <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/10.5.0/styles/stackoverflow-light.min.css" integrity="sha512-cG1IdFxqipi3gqLmksLtuk13C+hBa57a6zpWxMeoY3Q9O6ooFxq50DayCdm0QrDgZjMUn23z/0PMZlgft7Yp5Q==" crossorigin="anonymous" />
    <style>
      body {
        background: #f4f4f5;
        color: #020202;
      }
      .navbar-dark {
        background-image: -webkit-linear-gradient(top, #005f85 0, #002e49 100%);
        background-image: -o-linear-gradient(top, #005f85 0, #002e49 100%);
        background-image: linear-gradient(to bottom, #005f85 0, #002e49 100%);
        filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ff005f85', endColorstr='#ff002e49', GradientType=0);
        background-repeat: repeat-x;
      }
      .navbar-dark .navbar-nav .nav-link,
      .navbar-dark .navbar-nav .nav-link:focus { color: #fff }
      .navbar-dark .navbar-nav .nav-link:hover { color: #ffef68 }
      #wrapperlicious {
        margin: 0 auto;
        font: 0.9em 'Helvetica Neue', Helvetica, sans-serif;
        font-weight: normal;
        line-height: 1.5em;
        margin: 0;
        padding: 0;
      }
      #wrapperlicious h1 { font-size: 1.5em }
      #wrapperlicious h2 { font-size: 1.3em }
      #wrapperlicious h3 { font-size: 1.1em }
      #wrapperlicious h4 { font-size: 0.9em }
      #wrapperlicious h1, #wrapperlicious h2, #wrapperlicious h3,
      #wrapperlicious h4, #wrapperlicious dt {
        color: #020202;
        margin-top: 1em;
        margin-bottom: 1em;
        position: relative;
        font-weight: bold;
      }
      #wrapperlicious a { color: inherit; text-decoration: underline }
      #wrapperlicious #toc { text-decoration: none }
      #wrapperlicious a:hover { color: #2a2a2a }
      #wrapperlicious a img { border: 0 }
      #wrapperlicious :not(pre) > code {
        color: inherit;
        background-color: rgba(0, 0, 0, 0.04);
        border-radius: 3px;
        font: 0.9em Consolas, Menlo, Monaco, monospace;
        padding: 0.3em;
      }
      #wrapperlicious dd {
        margin: 0;
        margin-left: 2em;
      }
      #wrapperlicious dt {
        color: #2a2a2a;
        font-weight: bold;
        margin-left: 0.9em;
      }
      #wrapperlicious p {
        margin-bottom: 1em;
        margin-top: 1em;
      }
      #wrapperlicious li > p {
        margin-bottom: 0;
        margin-top: 0;
      }
      #wrapperlicious pre {
        border: 1px solid #c1c1c1;
        border-radius: 3px;
        font: 100% Consolas, Menlo, Monaco, monospace;
        margin-bottom: 1em;
        margin-top: 1em;
      }
      #wrapperlicious pre > code {
        display: block;
        background-color: #f6f6f6;
        font: 0.9em Consolas, Menlo, Monaco, monospace;
        line-height: 1.5em;
        text-align: left;
        white-space: pre;
        padding: 1em;
      }
      #wrapperlicious dl, #wrapperlicious ol, #wrapperlicious ul {
        margin-bottom: 1em;
        margin-top: 1em;
      }
      #wrapperlicious ul {
        list-style-type: square;
      }
      #wrapperlicious ul ul {
        margin-bottom: 0px;
        margin-top: 0px;
      }
      #footer {
        font-size: 0.8em;
        padding-top: 0.5em;
        text-align: center;
      }
      #more {
        display: inline;
        font-size: 0.8em;
      }
      #perldocdiv {
        background-color: #fff;
        border: 1px solid #c1c1c1;
        border-bottom-left-radius: 5px;
        border-bottom-right-radius: 5px;
        margin-left: auto;
        margin-right: auto;
        padding: 3em;
        padding-top: 1em;
        max-width: 960px;
      }
      #moduleversion { float: right }
      #wrapperlicious .leading-notice {
        font-style: italic;
        padding-left: 1em;
        margin-top: 1em;
        margin-bottom: 1em;
      }
      #wrapperlicious .permalink {
        display: none;
        left: -0.75em;
        position: absolute;
        padding-right: 0.25em;
        text-decoration: none;
      }
      #wrapperlicious h1:hover .permalink, #wrapperlicious h2:hover .permalink,
      #wrapperlicious h3:hover .permalink, #wrapperlicious h4:hover .permalink,
      #wrapperlicious dt:hover .permalink {
        display: block;
      }
    </style>
    <!-- Global site tag (gtag.js) - Google Analytics -->
    <script async src="https://www.googletagmanager.com/gtag/js?id=G-KVNWBNT5FB"></script>
    <script>
      window.dataLayer = window.dataLayer || [];
      function gtag(){dataLayer.push(arguments);}
      gtag('js', new Date());

      gtag('config', 'G-KVNWBNT5FB');
      gtag('config', 'UA-50555-3');
    </script>
  </head>
  <body>
    <nav class="navbar navbar-expand-md navbar-dark bg-dark justify-content-between">
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <a class="navbar-brand" href="https://perldoc.perl.org/">Perldoc Browser</a>
  <div class="collapse navbar-collapse" id="navbarNav">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item dropdown text-nowrap">
        <a class="nav-link dropdown-toggle" href="$^H.html#" id="dropdownlink-stable" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">5.35.0</a>
        <div class="dropdown-menu" aria-labelledby="dropdownlink-stable">
          <a class="dropdown-item" href="https://perldoc.perl.org/variables/$%5EH">Latest</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.38.2/variables/$%5EH">5.38.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.38.1/variables/$%5EH">5.38.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.38.0/variables/$%5EH">5.38.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.36.3/variables/$%5EH">5.36.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.36.2/variables/$%5EH">5.36.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.36.1/variables/$%5EH">5.36.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.36.0/variables/$%5EH">5.36.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.34.3/variables/$%5EH">5.34.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.34.2/variables/$%5EH">5.34.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.34.1/variables/$%5EH">5.34.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.34.0/variables/$%5EH">5.34.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.32.1/variables/$%5EH">5.32.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.32.0/variables/$%5EH">5.32.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.30.3/variables/$%5EH">5.30.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.30.2/variables/$%5EH">5.30.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.30.1/variables/$%5EH">5.30.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.30.0/variables/$%5EH">5.30.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.28.3/variables/$%5EH">5.28.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.28.2/variables/$%5EH">5.28.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.28.1/variables/$%5EH">5.28.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.28.0/variables/$%5EH">5.28.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.26.3/variables/$%5EH">5.26.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.26.2/variables/$%5EH">5.26.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.26.1/variables/$%5EH">5.26.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.26.0/variables/$%5EH">5.26.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.24.4/variables/$%5EH">5.24.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.24.3/variables/$%5EH">5.24.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.24.2/variables/$%5EH">5.24.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.24.1/variables/$%5EH">5.24.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.24.0/variables/$%5EH">5.24.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.22.4/variables/$%5EH">5.22.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.22.3/variables/$%5EH">5.22.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.22.2/variables/$%5EH">5.22.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.22.1/variables/$%5EH">5.22.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.22.0/variables/$%5EH">5.22.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.20.3/variables/$%5EH">5.20.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.20.2/variables/$%5EH">5.20.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.20.1/variables/$%5EH">5.20.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.20.0/variables/$%5EH">5.20.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.18.4/variables/$%5EH">5.18.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.18.3/variables/$%5EH">5.18.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.18.2/variables/$%5EH">5.18.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.18.1/variables/$%5EH">5.18.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.18.0/variables/$%5EH">5.18.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.16.3/variables/$%5EH">5.16.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.16.2/variables/$%5EH">5.16.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.16.1/variables/$%5EH">5.16.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.16.0/variables/$%5EH">5.16.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.14.4/variables/$%5EH">5.14.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.14.3/variables/$%5EH">5.14.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.14.2/variables/$%5EH">5.14.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.14.1/variables/$%5EH">5.14.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.14.0/variables/$%5EH">5.14.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.5/variables/$%5EH">5.12.5</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.4/variables/$%5EH">5.12.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.3/variables/$%5EH">5.12.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.2/variables/$%5EH">5.12.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.1/variables/$%5EH">5.12.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.12.0/variables/$%5EH">5.12.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.10.1/variables/$%5EH">5.10.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.10.0/variables/$%5EH">5.10.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.9/variables/$%5EH">5.8.9</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.8/variables/$%5EH">5.8.8</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.7/variables/$%5EH">5.8.7</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.6/variables/$%5EH">5.8.6</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.5/variables/$%5EH">5.8.5</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.4/variables/$%5EH">5.8.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.3/variables/$%5EH">5.8.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.2/variables/$%5EH">5.8.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.1/variables/$%5EH">5.8.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.8.0/variables/$%5EH">5.8.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.6.2/variables/$%5EH">5.6.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.6.1/variables/$%5EH">5.6.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.6.0/variables/$%5EH">5.6.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.005_04/variables/$%5EH">5.005_04</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.005_03/variables/$%5EH">5.005_03</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.005_02/variables/$%5EH">5.005_02</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.005_01/variables/$%5EH">5.005_01</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.005/variables/$%5EH">5.005</a>
        </div>
      </li>
      <li class="nav-item dropdown text-nowrap">
        <a class="nav-link dropdown-toggle" href="$^H.html#" id="dropdownlink-dev" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Dev</a>
        <div class="dropdown-menu" aria-labelledby="dropdownlink-dev">
          <a class="dropdown-item" href="https://perldoc.perl.org/blead/variables/$%5EH">blead</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.6/variables/$%5EH">5.39.6</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.5/variables/$%5EH">5.39.5</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.4/variables/$%5EH">5.39.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.3/variables/$%5EH">5.39.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.2/variables/$%5EH">5.39.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.39.1/variables/$%5EH">5.39.1</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.38.0-RC2/variables/$%5EH">5.38.0-RC2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.38.0-RC1/variables/$%5EH">5.38.0-RC1</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.11/variables/$%5EH">5.37.11</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.10/variables/$%5EH">5.37.10</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.9/variables/$%5EH">5.37.9</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.8/variables/$%5EH">5.37.8</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.7/variables/$%5EH">5.37.7</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.6/variables/$%5EH">5.37.6</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.5/variables/$%5EH">5.37.5</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.4/variables/$%5EH">5.37.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.3/variables/$%5EH">5.37.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.2/variables/$%5EH">5.37.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.1/variables/$%5EH">5.37.1</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.37.0/variables/$%5EH">5.37.0</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.11/variables/$%5EH">5.35.11</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.10/variables/$%5EH">5.35.10</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.9/variables/$%5EH">5.35.9</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.8/variables/$%5EH">5.35.8</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.7/variables/$%5EH">5.35.7</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.6/variables/$%5EH">5.35.6</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.5/variables/$%5EH">5.35.5</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.4/variables/$%5EH">5.35.4</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.3/variables/$%5EH">5.35.3</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.2/variables/$%5EH">5.35.2</a>
          <a class="dropdown-item" href="https://perldoc.perl.org/5.35.1/variables/$%5EH">5.35.1</a>
          <a class="dropdown-item active" href="$^H.html">5.35.0</a>
        </div>
      </li>
      <li class="nav-item dropdown text-nowrap">
        <a class="nav-link dropdown-toggle" href="$^H.html#" id="dropdownlink-nav" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Documentation</a>
        <div class="dropdown-menu" aria-labelledby="dropdownlink-nav">
          <a class="dropdown-item" href="../perl.html">Perl</a>
          <a class="dropdown-item" href="../perlintro.html">Intro</a>
          <a class="dropdown-item" href="../perl.html#Tutorials">Tutorials</a>
          <a class="dropdown-item" href="../perlfaq.html">FAQs</a>
          <a class="dropdown-item" href="../perl.html#Reference-Manual">Reference</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="../perlop.html">Operators</a>
          <a class="dropdown-item" href="../functions.html">Functions</a>
          <a class="dropdown-item" href="../variables.html">Variables</a>
          <a class="dropdown-item" href="../modules.html">Modules</a>
          <a class="dropdown-item" href="../perlutil.html">Utilities</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="../perlcommunity.html">Community</a>
          <a class="dropdown-item" href="../perlhist.html">History</a>
        </div>
      </li>
    </ul>
    <ul class="navbar-nav">
      <script>
        function set_expand (expand) {
          var perldocdiv = document.getElementById('perldocdiv');
          var width = window.getComputedStyle(perldocdiv).getPropertyValue('max-width');
          var expanded = (width == '' || width == 'none') ? true : false;
          if (expand === null) {
            expand = !expanded;
          }
          if ((expand && !expanded) || (!expand && expanded)) {
            perldocdiv.style.setProperty('max-width', expand ? 'none' : '960px');
            var button_classlist = document.getElementById('content-expand-button').classList;
            if (expand) {
              button_classlist.add('btn-light');
              button_classlist.remove('btn-outline-light');
            } else {
              button_classlist.add('btn-outline-light');
              button_classlist.remove('btn-light');
            }
          }
          return expand;
        }
        function toggle_expand () {
          var expand = set_expand(null);
          document.cookie = 'perldoc_expand=' + (expand ? 1 : 0) + '; path=/; expires=Tue, 19 Jan 2038 03:14:07 UTC';
        }
        function read_expand () {
          return document.cookie.split(';').some(function (item) { return item.indexOf('perldoc_expand=1') >= 0 });
        }
        if (document.readyState === 'loading') {
          document.addEventListener('DOMContentLoaded', function () {
            if (read_expand()) {
              set_expand(true);
            }
          });
        } else if (read_expand()) {
          set_expand(true);
        }
      </script>
      <button id="content-expand-button" type="button" class="btn btn-outline-light d-none d-lg-inline-block mr-2" onclick="toggle_expand()">Expand</button>
    <ul>
    <form class="form-inline" method="get" action="https://perldoc.perl.org/5.35.0/search">
      <input class="form-control mr-3" type="search" name="q" placeholder="Search" aria-label="Search">
    </form>
  </div>
</nav>

    <div id="wrapperlicious" class="container-fluid">
      <div id="perldocdiv">
        <div id="links">
          <a href="../variables.html">variables</a>
            / <a href="$^H.html">$^H</a>
          <div id="more">
            (<a href="$^H.txt">source</a>,
            <a href="$&lt;digits&gt;-($1,-$2,-...).html#$%5EH">CPAN</a>)
          </div>
        </div>
        <div class="leading-notice">
          You are viewing the version of this documentation from Perl 5.35.0.
            This is a development version of Perl.
        </div>
      <dl>

<dt id="$^H"><a class="permalink" href="$^H.html#$%5EH">#</a><a id="H"></a>$^H </dt>
<dd>

<p>WARNING: This variable is strictly for internal use only. Its availability, behavior, and contents are subject to change without notice.</p>

<p>This variable contains compile-time hints for the Perl interpreter. At the end of compilation of a BLOCK the value of this variable is restored to the value when the interpreter started to compile the BLOCK.</p>

<p>When perl begins to parse any block construct that provides a lexical scope (e.g., eval body, required file, subroutine body, loop body, or conditional block), the existing value of <code>$^H</code> is saved, but its value is left unchanged. When the compilation of the block is completed, it regains the saved value. Between the points where its value is saved and restored, code that executes within BEGIN blocks is free to change the value of <code>$^H</code>.</p>

<p>This behavior provides the semantic of lexical scoping, and is used in, for instance, the <code>use strict</code> pragma.</p>

<p>The contents should be an integer; different bits of it are used for different pragmatic flags. Here&#39;s an example:</p>

<pre><code>    sub add_100 { $^H |= 0x100 }

    sub foo {
	BEGIN { add_100() }
	bar-&gt;baz($boon);
    }</code></pre>

<p>Consider what happens during execution of the BEGIN block. At this point the BEGIN block has already been compiled, but the body of <code>foo()</code> is still being compiled. The new value of <code>$^H</code> will therefore be visible only while the body of <code>foo()</code> is being compiled.</p>

<p>Substitution of <code>BEGIN { add_100() }</code> block with:</p>

<pre><code>BEGIN { require strict; strict-&gt;import(&#39;vars&#39;) }</code></pre>

<p>demonstrates how <code>use strict &#39;vars&#39;</code> is implemented. Here&#39;s a conditional version of the same lexical pragma:</p>

<pre><code>    BEGIN {
	require strict; strict-&gt;import(&#39;vars&#39;) if $condition
    }</code></pre>

<p>This variable was added in Perl 5.003.</p>

</dd>
</dl>


      </div>
      <div id="footer">
        <p>Perldoc Browser is maintained by Dan Book (<a href="https://metacpan.org/author/DBOOK">DBOOK</a>). Please contact him via the <a href="https://github.com/Grinnz/perldoc-browser/issues">GitHub issue tracker</a> or <a href="mailto:dbook@cpan.org">email</a> regarding any issues with the site itself, search, or rendering of documentation.</p>

<p>The Perl documentation is maintained by the Perl 5 Porters in the development of Perl. Please contact them via the <a href="https://github.com/Perl/perl5/issues">Perl issue tracker</a>, the <a href="https://lists.perl.org/list/perl5-porters.html">mailing list</a>, or <a href="https://kiwiirc.com/client/irc.perl.org/p5p">IRC</a> to report any issues with the contents or format of the documentation.</p>


      </div>
    </div>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.slim.min.js" integrity="sha512-/DXTXr6nQodMUiq+IUJYCt2PPOUjrHJ9wFrqpJ3XkgPNOZVfMok7cRw6CSxyCQxXn6ozlESsSh1/sMCTF1rL/g==" crossorigin="anonymous"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.1/umd/popper.min.js" integrity="sha512-ubuT8Z88WxezgSqf3RLuNi5lmjstiJcyezx34yIU2gAHonIi27Na7atqzUZCOoY4CExaoFumzOsFQ2Ch+I/HCw==" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity="sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV+rV" crossorigin="anonymous"></script>
    <script src="../../highlight.pack.js"></script>
    <script>hljs.highlightAll();</script>
  </body>
</html>
